A device for mixing and/or communition is known from EP-A-0 203 598. It is know from EP-A-0 753 306 to use this device for the drying of plant extracts. The device described in this document is designed through mixing/communition as a vacuum contact drier for the use in the production of pharmaceutical active substances (API) and in the chemical and precision-chemical production and possesses a horizontally arranged heated cylinder with a heated agitator rotating in the latter about a horizontal axis.
The products to be dried are predominantly products of the pharmaceutical active substance industry and of the precision chemistry which contain, in addition to water, mostly organic solvents which are to be removed or are to be dried with a predetermined residual moisture content.
All the driers and methods known hitherto are characterized in that, in the first place, usually relatively long drying times occur. The product spectrum, that is to say the product properties, must in this case lie within a relatively narrow range, that is to say be highly standardized, so that in this case the products can be dried within acceptable times and in an at all reproduceable way. Some products, such as for example, liquids (solutions or suspensions), cannot be dried or can be dried only insufficiently and after adaptations (conversions).
Mostly, the wet products which are introduced into the drier for drying come from centrifugues or suction filters. The moisture contents of these wet products may fluctuate sharply, even within the same product. Moisture ranges of 20–50% by weight of moisture or more are possible. This wide fluctuation range makes it considerably more difficult, in conventional methods, to achieve similar or approximately identical drying times for the same material.
Physical properties of the products (viscosity, aggregation state solid or liquid, shrinkage), which occur or change in the course of the drying process, are an additional factor and in hitherto known systems often make it impossible to carry out drying completely to the desired final moisture or prolong the drying times to an extreme extent.
The dry products (finished products) must meet further requirements which are difficult to fulfill. These include as uniform a grain size and grain distribution (narrow size spectrum) as possible, so that the products can be made reproducible and standardizable.
These are requirements which have hitherto been fulfilled only inadequately. High additional outlay (redrying, milling, granulation) is often necessary in order to achieve these requirements.
A further important and often indispensable criterion in the production of active substances and precision-chemical products is the reproducibility of the drying results. What is meant by this is the achievement of virtually identical drying times for the same product which, however, originates as a whole from the plurality of batch dryings on the same apparatus. These properties include, inter alia, the final moisture, color and fineness of the material and the preservation of chemical and pharmaceutical effectiveness. Indirect properties are in this case the drying time and the energy consumption.